The present invention relates to compact disks, and more particularly, to a method for measuring the recording linear velocity of data recorded on a compact disk. This application for a method for measuring recording linear velocity of data on a compact disk is based on Korean Patent Application No. 96-15980, which is incorporated herein by reference for all purposes.
A compact disk (or "CD"), a mass medium, has a 12 cm diameter and a 680 Mb storage capacity. Numerous fine grooves are formed on a CD to store digitized data, e.g., audio data or computer data. The grooves are called "pits" and a row of pits are referred to as a "track". The tracks are formed as concentric circles, progressively from the center of the disk toward the periphery thereof. Typically, a CD has approximately 22,000 tracks. The distance between the tracks, i.e., the track pitch, is typically 1.6 .mu.m.
FIG. 1 is a plan view of a typical CD. FIG. 2 is a sectional view of the CD of FIG. 1, taken along section line II--II.
Referring to FIGS. 1 and 2, a CD 10 is an aluminum-coated synthetic resin disk of 12 cm diameter and 1.2 mm thickness. A 15 mm (inner diameter) pass through hole 10h is formed in the middle of the CD. The hole 10h is used to mount the CD 10 on a turntable of a spindle motor 31 in a disk drive. The CD 10 is divided into different areas. The CD 10 has a lead-in area 10a, also known as a TOC (Table Of Contents) area which contains summarized information regarding the contents of the CD. Typically, as in the case of an audio CD, the information contained in the TOC area includes the number of songs, the starting position of the songs, and the total performance time. A program area 10b is where data is recorded. A lead-out area 10c is reserved for recording of a signal for indicating the termination of a program, i.e., the end of the data.
According to the specifications of a typical audio CD, the recording linear velocity of the data is defined to be between 1.2 m/sec and 1.4 m/sec. A 1.2 m/sec recording linear velocity is typically employed when a great amount of data is to be recorded on a disk, whereas a 1.4 m/sec recording linear velocity is employed when relatively less data is recorded on a disk.
When the number of tracks from the current position to a target position on a disk are calculated, based on such a recording linear velocity, the distance between the current and target positions can vary according to the method of calculation. Accordingly, much time is taken up to access data by a pickup. Thus, the recording linear velocity of the data recorded on a disk should be accurately measured in order to accurately calculate number of tracks.
According to the conventional technology, the recording linear velocity of the data recorded on a disk has been measured according to the following two methods.
The first method is: after moving a pickup from one track position on a disk to the immediately previous track (i.e., in the reverse direction, from the outer track to the inner track), the time needed for the pickup to track around from the moved position back to the initial position is measured.
The second method is: after moving a pickup from one position on a disk to a position a predetermined number of tracks away (e.g., hundreds of tracks) in the reverse direction, the recording linear velocity of data is calculated based on the time necessary for the pickup to track around the initial position, and the number of the tracks.
However, in the first method, it takes a lot of time to complete the calculation of the recording linear velocity since the action of the pickup is performed at mono-multiple speed (i.e., the base reproduction speed, not doubled or tripled) in order to minimize errors. Also, precision in the movement by one track is required. Further, in the second method, since the pickup must move across many tracks, the necessary time becomes longer and error in the number of tracks becomes great.
Additionally, a stable servo action is required in either the stepwise track movement (first method) or the lump-sum track movement (second method), otherwise the resulting measurement is not reliable.